The present invention relates to methods of detecting carcinomas by measuring the level of a glycero compound, such as glycerol-3-phosphate, in a plasma, serum, or urine specimen from a patient. The method is particularly useful as a screening test for ovarian and breast carcinomas.
Carcinomas such as ovarian carcinoma, lung carcinoma, colon carcinoma, and breast carcinoma are among the most frequent causes of cancer death in the United States and Europe. Despite decades of cancer research, mortality rates among persons who contract cancer remain high. This dismal outcome is due, at least in part, to an inability to detect the carcinoma at an early stage of tumor development. When a carcinoma is detected at an early stage, survivability increases dramatically. For example, when ovarian carcinoma is diagnosed at an early stage, the cure rate approaches 90%. In contrast, the 5 year outlook for women with advanced disease remains poor with no more than a 15% survival rate. Thus, early diagnosis is one of the most effective means of improving the prognosis for carcinomas.
Frequently, however, detection of carcinomas depends upon the detection and inspection of a tumor mass which has reached sufficient size to be detected by physical examination. For instance, transvaginal sonography is the most sensitive of the currently available techniques used for detecting ovarian tumors. However, transvaginal sonography is non-specific, i.e. it will detect benign as well as malignant tumors. Accordingly, detection of an ovarian tumor by transvaginal sonography must be followed by a second diagnostic procedure which is able to distinguish benign tumors from malignant tumors. Moreover, transvaginal sonography is very expensive and, therefore, not useful as a screening procedure for large numbers of patients.
Typically, benign ovarian tumors are distinguished from malignant ovarian tumors by surgical procedures such as biopsy of the mass or aspiration of the mass and cytological examination of the cells that are surgically removed from the patient. However, these techniques are highly invasive, expensive, and in the case of aspiration can lead to release of cancerous cells into the peritoneum.
As can be seen from this example for ovarian cancer, several factors prevent the early detection and treatment of carcinomas. First, the carcinoma may be too small to be felt or seen on an x-ray or sonogram. Second, once the carcinoma is located, it may be mischaracterized as benign by the histologist examining a biopsy from the tumor. Third, the intensely invasive nature of these procedures prevents their use by patients and prohibits their use as regular screening techniques.
The detection of molecular markers of carcinogenesis and tumor growth can solve many of the problems which the physical examination of tumors have encountered. Samples taken from the patient for screening by molecular techniques are typically blood or urine, and thus require minimally invasive techniques. Thus, they can be used on a regular basis to screen for carcinomas. In addition, because molecular markers often appear before the tumor is of a detectable size, it is possible to detect carcinomas at very early stages in the progression of the disease. However, special processing of the samples is often required, and the molecular marker used is often of limited specificity and diagnostic value.
For instance, the antigenic determinant CA 125, which is a high molecular weight mucin-like glycoprotein, is the current serum biomarker of choice for screening for ovarian carcinomas. However, CA 125 testing suffers from two main limitations. First of all, it is not very sensitive. For example, elevated serum CA 125 levels, i.e. levels above the cut-off point of 35 U/ml, are present in fewer than 50% of the patients with Stage I ovarian carcinoma. Taylor, K. J. W. and Schwartz, P. E., xe2x80x9cScreening for Early Ovarian Cancer,xe2x80x9d Radiology, 192:1-10, 1994. In addition, CA 125 testing is not very specific. For example, approximately 25% of patients with benign gynecological diseases also have elevated serum levels of CA 125. Moreover, liver disease such as cirrhosis, even without ascites, elevates serum CA 125 levels above 35 U/ml. Taylor, K. J. W. and Schwartz, P. E., xe2x80x9cScreening for Early Ovarian Cancer,xe2x80x9d Radiology, 192:1-10, 1994.
Additionally, the level of lysophosphatidic acid (LPA) in the blood of patients has been used as an indicator of ovarian cancer and other gynecological carcinomas. For example, see the method disclosed in Xu, et al., U.S. Pat. Nos. 5,824,555, and 5,994,141. In this method, the plasma sample is first prepared from the blood of the patient. The sample may then be enriched by extracting lipids from the plasma sample with organic solvents in order to separate the LPA from other lipid components of blood. An LPA level of 0.1 xcexcM or greater is then assayed in the sample in order to diagnose the patient as having an ovarian carcinoma. Although LPA concentration is conventionally determined by gas chromatography, LPA may also be measured by enzymatically converting LPA to glycerol-3-phosphate, and then determining the level of glycerol-3-phosphate produced from LPA by an enzymatic cycling assay, see WO 00/23612. Although levels of LPA and other lysophospholipids in the blood have been shown in the blood of patients with carcinomas, see WO 98/43093, no similar instance has been shown for the endogenous levels of glycero compounds such as glycerol-3-phosphate.
The present invention provides a new, simple method for detecting the presence of carcinomas in a patient. The method comprises detecting the presence of an endogenous glycero compound such as glycerol-3-phospate (G3P) or a glycero compound derivative thereof (GPX) in a plasma, serum, or urine sample of the patient at levels which correlate with the presence of a carcinoma.
An embodiment of the method comprises: collecting a serum, plasma, or urine specimen from the patient, assaying for the presence of G3P, GPX, or a combination of glycero compounds in the specimen, and correlating the presence of the glycero compound at levels indicative of a carcinoma with the presence of the carcinoma in the patient. Glycero compounds suitable for assaying in the present invention include glycerol-3-phosphate (G3P), glycerophosphoinositol (GPI), glycerophosphocholine (GPC), glycerophosphoserine (GPS), glycerophosphoglycerol (GPG), and glycerophosphoethanolamine (GPE). In preferred embodiments of the invention, the xe2x80x9cglycero compoundxe2x80x9d assayed is a combination of these glycero compounds. A preferred embodiment of the method assays for the presence of the glycero compounds by an enzymatic cycling reaction utilizing glycerol-3-phosphate dehydrogenase and glycero-3-phosphate oxidase. If non-G3P glycero compounds are assayed in the invention, it is preferred that the enzymatic cycling reaction step be proceeded by an enzymatic step which cleaves non-G3P glycero compounds in the specimen to produce G3P.
The method of the present invention can be used to detect a broad range of carcinomas at an early stage, including breast carcinoma, ovarian carcinoma, cervical carcinoma, uterine carcinoma, endometrial carcinoma, peritoneal carcinoma, and fallopian tube carcinoma. Because the method is sufficiently sensitive to detect ovarian carcinoma in patients with early stage ovarian carcinoma and marginally invasive, the method is especially useful for screening patients for ovarian carcinomas. For the same reasons, the method is especially useful for screening patients for breast carcinomas, as current screening techniques (such as mammograms) are relatively expensive and uncomfortable for the patient.